Aromatic polycarbonates have been widely used in many fields as engineering plastics excellent in heat resistance, impact resistance, transparency, and the like.
Methacrylic resins obtained by polymerizing methacrylate esters are excellent in transparency and weather resistance and have been widely used as illumination devices, automobile parts, building-related materials, flat display materials, and the like.
As an industrial method for producing aromatic polycarbonates, the following methods (I) and (II) have been known:
(I) a method of causing interfacial polycondensation of bisphenol A with phosgene in the presence of an alkali catalyst; and
(II) a method of causing melt-polycondensation of bisphenol A with diphenyl carbonate (Patent Document 1).
According to the method (I), colorless and transparent polycarbonates can be obtained since the reaction proceeds at a low temperature. However, the method (I) has the following problems: toxic phosgene is used; inorganic salts such as sodium chloride produced by the reaction as by-products should be removed by washing; complex processes such as purification of the polymer and recovery of solvents after the reaction become necessary because of using solvents such as methylene chloride; and the like.
On the other hand, in the method (II), it is not necessary to use phosgene. Also, since it is not necessary to use any solvent, the separation of the polycarbonate from the reaction system is easy.
As a method for obtaining diphenyl carbonate to be used in the method (II), for example, the following methods have been known:
(II-1) a method of reacting phosgene with phenol to obtain diphenyl carbonate; and
(II-2) a method of obtaining diphenyl carbonate via an ester exchange reaction of a dialkyl carbonate with phenol and a disproportionation reaction (Patent Documents 2, 3).
However, in the method (II-1), there is a problem of using toxic phosgene.
On the other hand, in the method (II-2), it is not necessary to use phosgene.
As a method for obtaining a dialkyl carbonate to be used in the method (II-2), for example, the following methods have been known:
(II-2-1) a method of oxidizing ethylene to form ethylene oxide, reacting carbon dioxide produced as a by-product at that time with the ethylene oxide to obtain ethylene carbonate, and subsequently reacting the ethylene carbonate with an aliphatic alcohol to obtain a dialkyl carbonate and ethylene glycol; and
(II-2-2) a method of reacting carbon monoxide with an aliphatic alcohol to obtain a dialkyl carbonate; and
(II-2-3) a method of reacting acetone with chlorine molecule to obtain hexachloroacetone and hydrogen chloride and subsequently reacting the hexachloroacetone with an alcohol to obtain a dialkyl carbonate and chloroform (Patent Documents 4, 5).
However, the method (II-2-1) has a limitation that it is realized only at a place where there are facilities for oxidizing ethylene to form ethylene oxide and reacting carbon dioxide produced as a by-product at that time with the ethylene oxide. Also, in the method (II-2-1), the amount of production of the dialkyl carbonate varies depending on the demand for ethylene glycol.
The method (II-2-2) has a problem of using toxic carbon monoxide. Also, the method (II-2-2) has a limitation on reaction conditions and catalyst life.
Chloroform produced as a by-product in the method (II-2-3) can be utilized as a raw material for various fluorine-based materials. However, in the method (II-2-3), as compared with the demand for polycarbonates finally obtained by using the dialkyl carbonate as a raw material, the demand for the fluorine-based materials is small, so that the amount of production of the dialkyl carbonate is limited by the demand for the fluorine-based materials.
As an industrial method for producing a methacrylate ester, the following methods (i) to (v) have been known.
(i) a method of treating acetone cyanohydrin obtained from acetone and hydrogen cyanide with sulfuric acid and subsequently reacting the resultant with an alcohol;
(ii) a method of converting isobutylene or tert-butyl alcohol into methacrylic acid by a two-stage oxidation reaction, and esterifying the methacrylic acid;
(iii) a method of subjecting tert-butyl alcohol to vapor-phase oxidation to form methacrolein and subsequently obtaining a methacrylate ester through oxidative esterification by a liquid-phase catalytic reaction of the methacrolein in methanol;
(iv) a method of subjecting acetone cyanohydrin obtained from acetone and hydrogen cyanide to a hydration reaction to form α-hydroxyisobutyramide, converting α-hydroxyisobutyramide into methyl α-hydroxyisobutyrate by an amide-ester exchange reaction with methyl formate, and subsequently obtaining methyl methacrylate by a dehydration reaction of the methyl α-hydroxyisobutyrate; and
(v) a method of obtaining methyl propanoate from ethylene, methanol, and carbon monoxide and subsequently subjecting methyl propanoate to a vapor-phase condensation with formaldehyde to obtain methyl methacrylate.
However, the method (i) has the following problems: toxic hydrogen cyanide is used; hydrogen cyanide is available mainly as a by-product of acrylonitrile but there is a limitation on its availability; it is necessary to treat waste acid involved in the use of sulfuric acid; and it is possible to react the waste acid with ammonia to form ammonium sulfate but it takes a cost; and the like.
The method (ii) has a limitation on availability of isobutylene and tert-butyl alcohol.
The method (iii) has a limitation on availability of tert-butyl alcohol.
Since the method (iv) is a multi-stage process, it consumes large energy. Moreover, there is a limitation that it is realized only at a place where there are facilities capable of producing the formic acid derivative.
The method (v) has a problem of using toxic carbon monoxide. Moreover, the method (v) has a limitation of low conversion rate and catalyst life.